I am advised by Microsoft Support that Roll up aggregation for a parent table only works with simple column types.

This is a huge oversight in design. Any application dealing with financial transactions will most likely have a parent/child relationship where the child table has a calculated column, e.g. Number * price. The cild table will most likely have many rows which would need to be aggregated at the parent table, e.g. Orders to show a total order value.

Am astonished that dataverse does not support this scenario natively.